Most plant biomass materials, such as wood, are referred to as lignocellulosic material and comprise three main components, namely, cellulose, hemi-cellulose and lignin.    Cellulose: is a polysaccharide consisting of a linear chain of β(1→4) linked D-glucose units and will usually comprise 7,000 to 15,000 glucose molecules.    Hemi cellulose: is a polysaccharide related to cellulose but is derived from several sugars including glucose, xylose, mannose, galactose, rhamnose and arabinose and consists of shorter chains of around 200 sugar units.    Lignin is: a cross-linked macromolecule with molecular masses in excess of 10,000 and is relatively hydrophobic and aromatic in nature. Lignin is rich in the phenylpropanoids, such as p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol.
U.S. Pat. No. 5,730,837 describes the use of sulphuric acid in a 24% water, 44% methyl isobutyl ketone and 32% ethanol in the separation of biomass at 140° C. and resulting in an 18% yield of lignin based on the wood charged.
More recently, our co-pending International patent application PCT/GB2009/002731 describes a method of processing biomass which comprises the digestion of biomass material in an acidic aqueous medium, subjected to ultrasonic waves and separating the biomass into its constituents of lignin, hemi-cellulose and cellulose. This application describes the use of a variety of different acids, including an aliphatic dicarboxylic acid.
We have now found that, inter alia, the use of one particular acid, namely, oxalic acid, is advantageous in the treatment of biomass material in a pre-treatment stage and also in a subsequent digestion stage. We have also found a novel organosolv reagent which is suitable for the extraction of lignin and hemi-cellulose (monosaccharides) from biomass.